1. Field of the Invention
The present invention relates to a base material for lithography, and a method of producing a resist pattern that utilizes such a base material.
2. Description of the Related Art
In recent years, as the degree of integration of electronic devices has increased, the wavelength of exposure light used in the lithography processes during the production of semiconductor elements has continued to shorten. When this type of short wavelength exposure light is used to expose a photoresist layer formed on top of a substrate, the light reflected off the substrate increases, meaning that in some cases, the desired resist pattern cannot be formed. Accordingly, a so-called anti-reflective film (a base material layer for lithography) is formed between the substrate and the photoresist layer, and this anti-reflective film absorbs the reflected light, reducing and suppressing the effects of the reflected light.
Examples of conventional lithography base materials used for forming anti-reflective films include those disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 6-118631.
The lithography base materials disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 6-118631 comprise an acrylic resin with an anthracene ester unit of the structure shown in the chemical formula below (a resin component), and a cross linking agent such as glycoluril, dissolved in an organic solvent. 
wherein, R represents a single hydrogen atom or a single alkyl group, and w represents the molar fraction of the anthracene ester unit within the polymer, which is typically within a range from 0.1 to 1.0.
In a lithography process using this type of lithography base material, the lithography base material is applied to the top surface of a substrate, and is then subjected to heat treatment, causing the resin component to undergo a cross linking reaction that forms the lithography base material layer and prevents any mixing with the subsequently formed photoresist layer. The photoresist layer is then formed on top of this lithography base material, and selectively exposed. During exposure, light that passes through the photoresist layer is absorbed by the lithography base material layer, meaning that any effects arising from the type of reflected light described above can be suppressed. Subsequently, the photoresist layer is developed, yielding a resist pattern.
However, the base materials for lithography disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 6-118631 were unable to provide good film formation characteristics, while maintaining favorable light absorption characteristics (namely, a high absorption coefficient and a high refractive index). When the film formation characteristics of the lithography base material deteriorate, mixing with the photoresist layer develops, meaning the desired resist pattern cannot be obtained. In contrast, if the film formation characteristics were optimized, the targeted high level of light absorption is not achievable.
The present invention takes the above factors into consideration, with an object of providing a base material for lithography that provides superior film formation characteristics, while maintaining good light absorption characteristics.
The present invention incorporates the aspects [1] to [9] described below.
[1] A base material for lithography comprising a component (a), a component (b), and a component (c) described below:
(a) a cross linking agent;
(b) a copolymer comprising a (meth)acrylate ester unit represented by a general formula (1) shown below, 
wherein, R1 represents a hydrogen atom, a halogen atom, a hydroxyl group, a carboxyl group, or a hydrocarbon group of 1 to 5 carbon atoms that is substituted with at least one of a halogen atom, a hydroxyl group and a carboxyl group; X represents an alkyl chain of 1 to 4 carbon atoms; and R11 represents a hydrogen atom or a methyl group,
and a (meth)acrylate ester unit represented by a general formula (2) shown below, 
wherein, R2 represents a hydroxyl group, a carboxyl group, or a hydrocarbon group of 1 to 5 carbon atoms that is substituted with at least one of a hydroxyl group and a carboxyl group; Y represents xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94 or xe2x80x94SOxe2x80x94; n represents a number from 1 to 4; and R12 represents a hydrogen atom or a methyl group; and
(c) an organic solvent.
[2] A base material for lithography according to aspect [1] above, wherein the component (b) is a copolymer that also comprises a (meth)acrylate ester unit represented by a general formula (3) shown below, 
wherein, R3 represents a hydrocarbon group of 1 to 5 carbon atoms; and R13 represents a hydrogen atom or a methyl group.
[3] A base material for lithography according to either one of aspect [1] and aspect [2] above, wherein the component (a) is a nitrogen containing compound with an amino group and/or an imino group, and within all the amino groups and/or imino groups of the nitrogen containing compound, at least 2 hydrogen atoms are substituted with hydroxyalkyl groups and/or alkoxyalkyl groups.
[4] A base material for lithography according to aspect [3] above, wherein the component (a) is a condensation reaction product of the hydroxyalkyl group and/or alkoxyalkyl group with a monohydroxymonocarboxylic acid.
[5] A base material for lithography according to aspect [4] above, wherein in the monohydroxymonocarboxylic acid, the hydroxyl group and the carboxyl group are either bonded to the same carbon atom, or bonded to two adjacent carbon atoms.
[6] A base material for lithography according to aspect [5] above, wherein the monohydroxymonocarboxylic acid is at least one compound selected from a group consisting of mandelic acid, lactic acid, and salicylic acid.
[7] A base material for lithography according to any one of aspect [1] through aspect [6] above, further comprising a light absorbing component (d).
[8] A base material for lithography according to aspect [7] above, wherein the component (d) is at least one compound selected from a group consisting of anthracene based compounds, sulfone based compounds, sulfoxide based compounds and benzophenone based compounds containing at least 1 substituent group selected from a group consisting of hydroxyl group, hydroxyalkyl groups, alkoxyalkyl groups, and carboxyl groups.
[9] A method of producing a resist pattern comprising the steps of providing a lithography base material layer on top of a substrate by applying a base material for lithography according to any one of aspect [1] through aspect [8] above, and conducting heating to effect a cross linking reaction, providing a photoresist layer on top of the lithography base material layer, conducting light exposure, and developing the photoresist layer to form a resist pattern.
The base material for lithography according to the present invention provides superior film formation characteristics, while maintaining good light absorption characteristics.